Chemical Equations

Each card shows the equation visually — atoms colour-coded so you can count them. Open Atom Balance to verify conservation of mass.

(g) = gas(l) = liquid(s) = solid(aq) = dissolved in water
🔥Combustion

Burning Methane (Natural Gas)

Releases heat 🔥

methane + oxygen → carbon dioxide + water

C
H
H
H
H
CH₄(g)
+
2×
O
O
O₂(g)
→
C
O
O
CO₂(g)
+
2×
H
H
O
H₂O(l)

Complete combustion of natural gas. Releases a lot of energy — used in gas cookers, boilers, and power stations. Always produces CO₂ and H₂O when there is enough oxygen.

🔥Combustion

Burning Hydrogen (Clean Fuel)

Releases heat 🔥

hydrogen + oxygen → water

2×
H
H
H₂(g)
+
O
O
O₂(g)
→
2×
H
H
O
H₂O(l)

The cleanest possible fuel — the only product is water. Hydrogen fuel cells in cars use this reaction. The squeaky-pop test detects H₂ gas.

🔥Combustion

Burning Magnesium

Releases heat 🔥

magnesium + oxygen → magnesium oxide

2×
Mg
Mg(s)
+
O
O
O₂(g)
→
2×
Mg
O
MgO(s)

Burns with a dazzling white light — never look directly at it. The white ash (MgO) has a much higher melting point than the original metal. Used in fireworks and flares.

💧Neutralisation

Acid + Alkali (Neutralisation)

Releases heat 🔥

hydrochloric acid + sodium hydroxide → sodium chloride + water

H
Cl
HCl(aq)
+
Na
O
H
NaOH(aq)
→
Na
Cl
NaCl(aq)
+
H
H
O
H₂O(l)

The H⁺ ion from the acid meets OH⁻ from the alkali to form water. The remaining Na⁺ and Cl⁻ form salt. Evaporate the water → you get table salt crystals.

⚡Decomposition

Thermal Decomposition of Limestone

Absorbs heat ❄️Heat (900 °C)

calcium carbonate → calcium oxide + carbon dioxide

Ca
C
O
O
O
CaCO₃(s)
→
Ca
O
CaO(s)
+
C
O
O
CO₂(g)

Strong heating breaks limestone apart. The quicklime (CaO) produced is used in cement, glass and steel. This is why cement factories emit CO₂.

⚡Electrolysis

Electrolysis of Water

Absorbs heat ❄️Electricity

water → hydrogen + oxygen

2×
H
H
O
H₂O(l)
→
2×
H
H
H₂(g)
+
O
O
O₂(g)

Electricity splits water into hydrogen and oxygen. Hydrogen collects at the cathode (−), oxygen at the anode (+). The volume of H₂ is always exactly twice that of O₂.

⚡Decomposition

Decomposition of Hydrogen Peroxide

Releases heat 🔥MnO₂ catalyst

hydrogen peroxide → water + oxygen

2×
H
H
O
O
H₂O₂(aq)
→
2×
H
H
O
H₂O(l)
+
O
O
O₂(g)

MnO₂ (manganese dioxide) is a catalyst — it speeds up the reaction without being used up. The oxygen produced re-lights a glowing splint.

⚗️Acid + Metal

Zinc + Sulfuric Acid

Releases heat 🔥

zinc + sulfuric acid → zinc sulfate + hydrogen

Zn
Zn(s)
+
H
H
S
O
O
O
O
H₂SO₄(aq)
→
Zn
S
O
O
O
O
ZnSO₄(aq)
+
H
H
H₂(g)

Zinc is more reactive than hydrogen so it displaces it from the acid. The H₂ gas produced makes a squeaky pop with a lit splint. Zinc sulfate stays in solution.

⚗️Acid + Metal

Magnesium + Hydrochloric Acid

Releases heat 🔥

magnesium + hydrochloric acid → magnesium chloride + hydrogen

Mg
Mg(s)
+
2×
H
Cl
HCl(aq)
→
Mg
Cl
Cl
MgCl₂(aq)
+
H
H
H₂(g)

More vigorous than zinc because magnesium is higher in the reactivity series. The ribbon dissolves rapidly, producing bubbles of hydrogen gas.

🔗Synthesis

Haber Process (Making Ammonia)

⇌ Reversible450 °C · 200 atm · Fe catalyst

nitrogen + hydrogen ⇌ ammonia

N
N
N₂(g)
+
3×
H
H
H₂(g)
⇌
2×
N
H
H
H
NH₃(g)

The ⇌ arrow means it is reversible — both forward and backward reactions happen at once. An iron catalyst, high pressure (200 atm) and temperature (450 °C) are used. Ammonia is the basis of fertilisers.

Conservation of Mass

In every chemical reaction, atoms are never created or destroyed — they only rearrange. This means the total number of each atom must be identical on both sides of the arrow. That’s why equations must be balanced with coefficients (the big numbers in front). Open the Atom Balance Check on any reaction above to see this in action.

Reactants

What you start with

→ (arrow)

Reaction takes place

Products

What you end up with